I'm not sure it really makes a difference. An unpapered Appendix is a QH/TB mix. And many papered QH's have a significant amount of TB blood- take the papers away and it'd be considered a QH/TB mix as legitimately as a "grade" QH.
It's hard to tell. I have to say some body features don't look quarter horse to me, but there is always the exception. I absolutely love quarter horses, so I would love to imagine its a full quarter horse, but I myself would lean to likely be a cross. Beautiful horse either way. You must have paid a great price to.